In a conventional magnetic recording system, the rotation of the rigid magnetic disk causes a transducer or magnetic recording head to be hydrodynamically lifted above the surface of the recording medium. The hydrodynamic lifting phenomena results from the flow of air produced by the rotating magnetic disk. This airflow causes the head to "fly" above the disk surface. Of course, when the rotation of the magnetic disk stops or slows, the head element is deprived of its aerodynamic buoyancy and lands on the surface of the disk.
Magnetic heads typically comprise a rectangular slider body onto which is attached a transducer device along one portion of the slider body. Normally, sliders are made of various ceramic materials. For instance, a composition of alumina and titanium-carbide is one of the more common slider materials in use today due to its relative wear resistance. A variety of other materials have also been used as well. There are typically two types of transducers for magnetic recording, thin film or magneto-resistive (MR). Thin-film transducers can read or write. An MR transducer can only read. Hence a second thin film transducer must be used in combination with an MR transducer for full read/write capabilities.
A primary goal of hard disk drives is to provide maximum recording density in the hard disk. It has been found that the recording density that can be achieved using a magnetic recording transducer depends, in part, on the distance between the recording medium of the hard disk and the magnetic recording transducer. A related goal is to increase reading efficiency or reduce read errors, while increasing recording density. Problems associated with attaining these goals may vary depending upon whether the drive utilizes a thin film transducer for both reading and writing, or a magneto-resistive transducer for reading and a thin film head for writing.
From a writing or recording density standpoint, the transducer is ideally maintained in direct contact with the recording medium of a hard disk. Recording density decreases as the write transducer is elevated above the disk surface. By providing zero separation distance between the magnetic recording transducer of the slider and the disk, high magnetic recording densities are achieved. However, the hard disk typically spins at about or in excess of 4,000 r.p.m. and the friction caused by the continuous direct contact between the slider and the transducer, on one hand, and the recording medium, on the other hand, can cause unacceptable wear in the recording medium, the slider and the transducer. Wear occurring in the recording medium can result in a loss of data. Wear occurring in the transducer can result in complete failure of the recording transducer requiring replacement of the slider housing the transducer, as well as loss of data.
A common approach to protecting the head/disk interface from excessive wear has been to coat the surface of the disk with a liquid lubricant. However, this can create an accumulation of debris on the head, including the lubricant and dust or dirt from the surrounding environment. Accumulation of such debris around the contact surface of the head leads to signal modulation caused by particle induced fluctuations in the head. Accumulation of debris and other particulate matter can also create a dramatic increase in the wear rate as the debris is captured in the friction zone between the slider and the disk. The presence of any liquid lubricant in the zone can magnify this effect dramatically.
To prevent undue wear of the recording medium and the slider and/or transducer while still maintaining acceptable recording density, the bottom surface of the slider is typically configured as an air bearing surface. High speed rotation of the disk causes a stream of air to flow along the surface of the disk. The air-bearing surface of the slider interacts with the flow of the air causing the slider to float about the hard disk surface. Hence, while the disk is spinning and the slider is positioned adjacent to the disk, the slider floats slightly above the disk, thereby substantially eliminating wear to either the disk or to the slider.
Although the conventional air-bearing surface slider design has been effective in preventing wear of the slider and/or transducer and the recording medium, optimum recording densities have been lost due to separation between the recording medium and the magnetic recording transducer of the slider.
From the standpoint of reading data from a magnetic disk, and similar to recording, reading efficiency decreases the farther the read element is from the disk. Because the signal to noise ratio decreases with increasing distance between the transducer and the disk, moving the transducer closer to the disk increases data storage bit density. Moreover, because MR transducers are more sensitive than thin film read elements, an MR transducer will read more efficiently, with less errors, than a thin film head at the same distance above the disk.
Conventional magneto-resistive elements disposed on sliders are designed with air bearing surfaces to fly above the surface of a rigid rotating magnetic recorded disk. Current disk drives with MR heads operate at an average head to disk physical spacing of approximately 40 nanometers, with distribution ranging up to 75 nanometers or more. This range of spacing is required to account for slider and disk drive manufacturing tolerances, such as in the actuator and disk/spindle interface, and environmental conditions such as altitude and temperature, which would cause the slider to fly too low and make contact with the rigid disk. Contact of the magneto-resistive MR transducer with the disk surface has proven to cause an undesirable thermal transient due to friction, commonly referred to as thermal asperity. Thus, unlike inductive heads which are able to tolerate disk contacts without generating signal transients, use of MR heads has required the MR heads to fly above the disk surface resulting in less efficient recording density.
When a hard drive is at rest, the slider is in contact with the disk. This creates a static friction between the slider and the disk. During the operation, this static friction must be overcome to allow the disk to spin. As expected, high static friction results in a large amount of power consumption by the hard disk drive to overcome this static friction. One method of reducing the hard disk drive's power consumption is to lower the static friction between the slider and the disk. Typically, this reduction in static friction is achieved by intentionally texturing the disk. This texturing introduces imperfection on the disk creating asperties or roughness on the surface of the disk. The asperities reduce the static friction by lowering the amount of surface area that is in contact with the slider. Unfortunately, however, the asperities vary the distances between the recording head and the recording medium which can effect reading and writing operations.
For a hard disk drive utilizing an (MR) transducer, a direct contact between the disk and the MR transducer can result in thermal transients which can result in incorrect data transfer. Thus, it is crucial to maintain separation between the disk and the MR transducer in a hard disk drive having a contact slider. But the disk asperities which are intentionally introduced to reduce the static friction can result in actual contact between the MR transducer and the disk, depending on the positioning of the MR transducer, causing transducer wear or thermal transients that can result in a complete failure of the recording transducer or inaccurate data transfer. One method of reducing this potential problem is to burnish the disk to remove asperities.
Based on the foregoing, a desirable solution would be to utilize a flying MR head transducer with as little spacing as possible between the disk surface and the transducer. With flying heads, however, the height is influenced in large part by the quality of the manufacturing process. Manufacturing tolerance includes the manufacturability of components such as the crown, camber, twist, etch depths of the slider, head-gimble interface, assembly tolerances and the very process of stacking and swaging parts together. If a precise suspension and alignment mechanism is required, such as with the transducer spaced only a few nanometers above the disk surface, the overall mechanical tolerances of various components must be correspondingly more precise. Such precision would be not only mechanically difficult, but exceedingly expensive.
Therefore, there is a need for a relatively simple and inexpensive contact slider with an MR transducer placed above the recording medium with a reduced static friction between the slider and a recording medium. There is also a need for burnishing the disk to reduce the disk asperities to levels below the MR transducer height.